1. Field of the Invention
The present invention relates to a horizontal linearity correction coil to be used for a television receiver or the like.
2. Description of the Related Art
In a television receiver using a cathode ray tube which has a wide deflection angle of 112 degrees and which has a plane fluorescent screen called a flat face, when a lattice-shaped cross hatch pattern 1 is displayed on the screen as shown in FIG. 4, a distortion occurs to widen the distance in the horizontal direction of the screen as shown by 1a and 1b at portions between the center and the left end portion and between the center and the right end portion of the screen.
As shown in FIG. 5, a horizontal deflection current 2a is linear with respect to time t (that is, this current shows a constant change rate with the change of time), and cathode rays (electron beams) of a cathode ray tube 3 shown in FIG. 6 are electromagnetically deflected at a constant angle (.theta..sub.a1 =.theta..sub.a2 =.theta..sub.a3 =.theta..sub.a4). Since the fluorescent screen of the cathode ray tube 3 is plane, the displayed positional dimensions of the fluorescent screen of the cathode ray tube 3 become l.sub.a1 .noteq.l.sub.a2 .noteq.l.sub.a3 .noteq.l.sub.a4.
In order to correct this distortion, first and second linearity correction coils 6 and 7 are connected in series to a horizontal deflection coil 5 which is connected to a horizontal deflection output circuit 4 and a capacitor 8 is connected to this second horizontal linearity correction coil 7 so as to form a horizontal defection circuit as the circuit is shown in FIG. 7.
FIG. 8 shows the electrical characteristics of the first and second horizontal linearity correction coils 6 and 7. The characteristic of the first horizontal linearity correction coil 6 is designated by L.sub.6 and the characteristic of the second horizontal linearity correction coil 7 is designated by L.sub.7. The characteristic L.sub.6 of the first horizontal linearity correction coil 6 shows a peak value of inductance in the middle between "0" of a horizontal deflection current I.sub.H and a maximum value at the minus side. The characteristic L.sub.7 of the second horizontal linearity correction coil 7 shows a peak value of inductance in the middle between "0" of the horizontal deflection current I.sub.H and a maximum value at the plus side. Thus, the peak value of the characteristic L.sub.6 is larger than the peak value of the characteristic L.sub.7.
In order to obtain a characteristic designated by L.sub.8, by combining the characteristic L.sub.6 and the characteristic L.sub.7, the first and second horizontal linearity correction coils 6 and 7 are connected in series, and the horizontal deflection current 2a is corrected as shown by 2b as shown in FIG. 5 so that the change rate of the horizontal deflection current with respect to time is changed. Particularly, the change rates of the horizontal deflection current become smaller at the positions of the intermediate portions between the center portion and the left end portion and between the center portion and the right end portion of the fluorescent screen of the cathode ray tube. The electromagnetic deflection angles with respect to the time change of the cathode rays (electron beams) of the cathode ray tube 3 become .theta..sub.b1 .noteq..theta..sub.b2 .noteq..theta..sub.b3 .noteq..theta..sub.b4. However, the positional dimensions displayed on the fluorescent screen of the cathode ray tube 3 become l.sub.b1 =1.sub.b2 =1.sub.b3 =l.sub.b4, so that the distortion is corrected as shown in FIG. 9. Consequently, when the lattice-shaped cross hatch pattern 1 is displayed on the screen, a constant distance can be maintained as shown in FIG. 10.
The first and second horizontal linearity correction coils 6 and 7 have the structures as shown in FIG. 11 and FIG. 12, respectively.
That is, the first horizontal linearity correction coil 6 comprises a first ferrite magnetic core 9 of drum type, a first winding 11 wound around the first ferrite magnetic core 9 and a first ferrite magnet 13 combined at one of flanges 9a of the first ferrite magnetic core 9. Similarly, the second horizontal linearity correction coil 7 comprises a second ferrite magnetic core 10 of drum type, a second winding 12 wound around the second ferrite magnetic core 9 and a second ferrite magnet 13 combined at one of flanges 10a of the second ferrite magnetic core 9.
The first horizontal linearity correction coil 6 shown in FIG. 11 is structured to form the first ferrite magnetic core 9 with the diameter of a first winding core portion 9b at the rate of 0.33 to 0.35 of the diameter of the first flange 9a. The second horizontal linearity correction coil 7 shown in FIG. 12 is structured to form the second ferrite magnetic core 10 with the diameter of a second winding core portion 10b at the rate of not larger than 0.3 of the diameter of the second flange 10a so that a magnetic saturation is generated in small inductance.